In the evaporation of high melting point metals, such as uranium for uranium enrichment as discussed in U.S. Pat. No. 3,772,519, incorporated herein by reference, the evaporated material has typically been heated in a crucible by furnace or electron beam techniques and the material to be vaporized (evaporant) then is emitted from hot surface regions of the molten metal. In so heating, it is likely that all, or nearly all, of the evaporant contained in the melting chamber or crucible becomes liquid due to the rapid heat transfer through the material from several phenomena, a significant one being convection currents in the molten material. The rapid convection of heat away from the surface of the molten evaporant reduces evaporation efficiency very substantially, and in the case of uranium, forces a hot, reactive metal up against the crucible walls where corrosion can lead to their more rapid degradation.
It is known and has been suggested that crucibles may be lined with a relatively inert liner to reduce the effect of the corrosive molten liquid on the crucible edges, see for example U.S. Pat. No. 3,437,328. Such liners, however, do not overcome the problem of heat transfer away from the point of evaporation and the resulting loss in efficiency.